Bidirectional Forwarding Detection

Bidirectional Forwarding Detection (BFD) is used to detect faults between two routers across a link, even if the physical link does not support failure detection. TNSR uses UDP as a transport for BFD between directly connected routers (single hop/next hop) as described in RFC 5880 and RFC 5881.

Each BFD session monitors one link. Multiple BFD sessions are necessary to detect faults on multiple links. BFD sessions must be manually configured between endpoints as there is no method for automated discovery.

BFD supports session authentication using SHA1 and we recommend using authentication when possible to secure BFD sessions.

When using BFD, both endpoints transmit “Hello” packets back and forth between each other. If these packets are not received within the expected time frame, the link is considered down. Links may also be administratively configured as down, and will not recover until manually changed.